Damp Proofer
Tax & MTD Guide
CIS deductions and refunds, allowable expenses on tools, van and PPE, record-keeping, VAT and MTD explained for UK self-employed damp proofing specialists.
Estimate your tax as a self-employed damp proofer
Adjust the figures to see your estimated Income Tax and Class 4 National Insurance for the year.
Total turnover before expenses
Under £1,000 we use the trading allowance automatically
Estimated tax bill
£4,272
11.2% effective rate for 2026/27
- Income tax
- £3,286
- Class 4 NI
- £986
Take-home pay
£24,728
after tax, NI and expenses
This is an estimate using GOV.UK rates for 2026/27, not your official tax calculation. TapTax is MTD-compatible, so you can connect to HMRC and file the real figures in a couple of taps.
- You pay Income Tax and National Insurance on your profit, your damp proofing income minus allowable expenses, not on what lands in your bank account before deductions.
- Most damp proofers work as CIS subcontractors, so contractors deduct 20% from your labour (30% if unregistered); this is advance tax and almost always produces a Self Assessment refund.
- Your biggest deductions are the van, injection and drilling equipment, damp-proof cream and membranes, PPE such as respirators and FFP3 masks, and the materials you buy for each job.
- MTD for Income Tax starts April 2026 above £50,000 of gross income, April 2027 above £30,000, and April 2028 above £20,000, tested on turnover not profit.
- Register for CIS and keep every deduction statement, materials receipt and mileage log; sloppy records are what turn a healthy refund into an underpayment.
Damp proofing is a materials-and-labour trade with one tax quirk that dominates everything else: the Construction Industry Scheme. You drill, inject damp-proof cream, hack off blown plaster, fit membrane and re-render, then invoice a builder or property maintenance firm who deducts 20% before they pay you. That deduction is not a charge you have lost. It is your own Income Tax paid in advance, and because it ignores your personal allowance and every tool, litre of cream and mile in the van, it is almost always more than you actually owe. The job of your Self Assessment return is to claim the difference back.
This guide covers how a damp proofer really earns and spends: CIS deductions and the refund they create, the specific kit and consumables you can claim, the van, PPE, and the records that keep HMRC happy.
How Tax Works for a Self-Employed Damp Proofer
As a sole trader you pay Income Tax on profit, which is your total damp proofing income minus allowable expenses. For 2026/27 the personal allowance covers the first £12,570, then you pay 20% to £50,270, 40% to £125,140 and 45% above, with the personal allowance tapering away between £100,000 and £125,140 to create an effective 60% band. Class 4 National Insurance is 6% on profit between £12,570 and £50,270 and 2% above, with Class 2 NIC settled through Self Assessment.
Scottish damp proofers pay Scottish Income Tax on their profit through six bands (19%, 20%, 21%, 42%, 45% and a 48% top rate) and carry an S-prefixed tax code, while National Insurance stays UK-wide. Welsh workers have a C-coded tax code at rates currently matching the rest of the UK. If you also hold a part-time PAYE job and your code looks off, run it through the tax code checker before it costs you.
CIS: The Deduction That Becomes a Refund
If you carry out construction work as a subcontractor, including damp proofing, tanking and remedial plastering, you fall inside the Construction Industry Scheme whenever your client is a contractor (a builder, a developer, a maintenance company). Before paying you, they verify you with HMRC and deduct tax from your labour.
- CIS deduction
- Under the Construction Industry Scheme, contractors deduct money from a subcontractor's labour payment and pass it to HMRC as advance Income Tax and National Insurance. The rate is 20% if you are registered for CIS and 30% if you are not. The deduction applies only to the labour element of your invoice, never to materials such as damp-proof cream, membrane, sand, cement or plaster, so always split labour and materials clearly on every invoice to avoid being over-deducted.
Two points decide how much you keep. First, register for CIS, because the unregistered rate is 30% rather than 20%, an extra 10% of your labour tied up with HMRC until you file. Second, itemise materials separately on every invoice, because CIS is deducted on labour only. Lump a £600 materials cost in with labour and you hand over an unnecessary £120 in deductions you then have to reclaim.
Because the deduction is taken before your personal allowance and any expenses, it almost always exceeds your real liability, so most damp proofers are owed money. Use the CIS tax calculator to estimate your refund, and read our full guide to being a CIS subcontractor for how to register, verify and reconcile deductions at year end.
Allowable Expenses for Damp Proofers
An expense is allowable when incurred wholly and exclusively for the business. For a damp proofer the list is dominated by the van, specialist equipment, consumable materials and the PPE the job demands.
| Expense | What qualifies | Notes |
|---|---|---|
| Van and vehicle | Mileage at HMRC rates, or actual fuel, insurance, repairs, MOT and a capital allowance on the van | Pick one method per vehicle and stick to it |
| Injection equipment | Damp-proof injection guns, hand pumps, applicators, hoses | Larger kit claimed via the Annual Investment Allowance |
| Drills and bits | SDS hammer drills, masonry and diamond bits, dust extraction | Replaced often; keep receipts |
| Damp meters and tools | Protimeter-style moisture meters, hygrometers, hacking tools, hawks, floats and trowels | Calibration costs are deductible too |
| Materials and consumables | Damp-proof cream, DPC membrane, tanking slurry, salt-neutraliser, renovating plaster, sand, cement | Recharge to the client and keep them out of CIS labour |
| PPE | FFP3 / respirator masks, replacement filters, goggles, gloves, knee pads, overalls, ear defenders, work boots | Genuinely protective gear is allowable; everyday clothing is not |
| Site power and lighting | Work lamps, extension leads, generators, transformers | Running costs and equipment both qualify |
| Protection | Dust sheets, floor protection, masking, skip and waste disposal | Deductible per job |
| Home-office and phone | Flat-rate working-from-home allowance or a fair proportion of costs; business share of mobile | Quoting, invoicing and admin done from home |
| Insurance and certification | Public liability and tool insurance, CSCS card, PCA or trade-body membership | Cover and cards relevant to the trade are allowable |
| Training | Courses that update existing damp proofing or remedial skills | A brand-new trade qualification is not allowable |
| Accountancy and bank fees | Bookkeeping, Self Assessment, business banking | Fully deductible |
The Van and Mileage in Detail
The van is usually a damp proofer's second-largest cost after materials. You have two methods. The simplified flat rate claims 45p per business mile for the first 10,000 miles and 25p thereafter, needing only a mileage log and no fuel receipts. Or you claim actual running costs, fuel, insurance, servicing, repairs and a capital allowance on the van, scaled to business use. High mileage between regional jobs often favours actual costs; a local operator may prefer the simplicity of mileage. Work it out both ways once, then commit to one method per vehicle.
PPE and What You Cannot Claim
Damp work means dust, spores and chemicals, so respirators, FFP3 masks and replacement filters, goggles, gloves and overalls are clearly allowable. Not allowable: everyday clothing worn under the overalls, the private share of dual-use costs like your mobile or van, fuel for personal trips, or fines. For any tool you also use at home, claim only the business proportion.
Record-Keeping That Protects Your Refund
Your refund depends on proving both income and costs, so records matter more for a CIS trade than almost any other. Keep every CIS deduction statement (your proof of tax already paid), all materials receipts tagged to the job, a mileage log or fuel receipts, sales invoices that split labour and materials, and equipment and PPE receipts. A shoebox of faded receipts is how a refund quietly becomes an underpayment. Snap a photo of each receipt the day you get it and the year-end reconciles itself.
Worked Example: A Damp Proofer on £45,000
Take a self-employed damp proofing subcontractor with £45,000 of income for the year, of which £33,000 is labour (subject to CIS) and £12,000 is materials recharged to contractors.
Income: £45,000 (labour £33,000, materials £12,000)
CIS already deducted: 20% of £33,000 labour = £6,600 paid to HMRC at source
Allowable expenses:
- Materials and consumables (cream, membrane, plaster): £12,000
- Van actual running costs and capital allowance: £4,500
- Injection kit, drills, meters and tools: £1,800
- PPE, respirator filters and protection: £700
- Insurance, CSCS and trade membership: £600
- Home-office, phone and accountancy: £900
- Total expenses: £20,500
Taxable profit: £45,000 minus £20,500 = £24,500
Income Tax: £24,500 minus £12,570 = £11,930 at 20% = £2,386
Class 4 NIC: £11,930 at 6% = £716
Tax and NIC due: £3,102. Against this you have already paid £6,600 through CIS, so HMRC refunds the difference of roughly £3,498. That refund is exactly why filing on time matters. Run your own figures through the sole trader tax calculator before you file.
For a damp proofer, your CIS deductions are your own money sitting with HMRC. Itemise materials, register at 20% not 30%, and file on time, and that money comes home as a refund.
VAT and the Domestic Reverse Charge
You must register for VAT once taxable turnover exceeds £90,000 in any rolling 12-month period. A one-person damp proofing business taking on large remedial contracts with materials included can reach this, so watch your rolling total rather than the tax-year figure.
There is a construction-specific twist. The VAT domestic reverse charge applies to most construction services supplied between VAT-registered businesses inside CIS. In plain terms, when you subcontract to a VAT-registered builder, you do not charge VAT; the contractor accounts for it instead, and you note on the invoice that the reverse charge applies. This protects your cash flow but changes how you invoice, so if you cross the threshold, get the wording right before you raise a single VAT invoice.
MTD for Income Tax: What Changes for Damp Proofers
Making Tax Digital for Income Tax Self Assessment replaces the once-a-year return with quarterly digital submissions and a year-end finalisation. The thresholds are based on gross income, not profit:
- April 2026: Combined trading and property income over £50,000
- April 2027: Over £30,000
- April 2028: Over £20,000
Because the test is on gross turnover including recharged materials, a damp proofer can pass the threshold sooner than profit suggests. Instead of bagging up a year of CIS statements each January, you record each invoice, deduction and materials cost digitally as it happens and send HMRC a quarterly summary, then finalise the year and settle your CIS refund. For a trade with deductions taken at source all year, continuous records make the refund quicker and the year-end far less stressful. Our guide to MTD for sole traders walks through the quarterly rhythm in practice.
Common Mistakes Damp Proofers Make
Not registering for CIS. Staying unregistered means a 30% deduction instead of 20%, tying up an extra tenth of your labour with HMRC until you file.
Lumping materials in with labour. CIS is deducted on labour only. Mix in cream, membrane and plaster and you get over-deducted, then have to reclaim it.
Losing CIS deduction statements. These are your proof of tax already paid; without them you cannot evidence your refund.
Mixing van methods. You cannot switch between mileage and actual costs for the same vehicle mid-life. Choose once and keep records to match.
Filing late. The sooner you file, the sooner the money you overpaid through CIS comes back. Late filing just lends HMRC your cash for longer.
People also ask
Damp proofer income and Making Tax Digital
If you work for yourself, Making Tax Digital for Income Tax applies to you from 6 April 2026 if your qualifying income is over £50,000, and from 6 April 2027 if it is over £30,000. TapTax keeps your digital records and sends your quarterly updates to HMRC, and it is MTD-compatible.
Start freeQuarterly expenses under MTD: the £90,000 rule
If your annual business turnover is £90,000 or less, HMRC lets you report a single consolidated expenses total in each Making Tax Digital quarterly update instead of breaking expenses down into itemised categories. Most self-employed damp proofer businesses are under this threshold, so a quarterly update can be as simple as two figures: total income and total expenses. You still need to keep digital records of each individual expense - the relaxation only changes how much detail goes into the quarterly update itself.
Related calculators and guides
More self-employed tax guides
Frequently asked questions
Why do I get a CIS deduction taken off my damp proofing invoices?
When you work as a subcontractor for a builder, main contractor or property maintenance firm, the Construction Industry Scheme makes them deduct tax from your labour before they pay you. If you are CIS-registered the deduction is 20%; if not it is 30%. The deduction only applies to your labour, not to materials like damp-proof cream, membrane or plaster. Those deductions are advance payments of your Income Tax and NIC, and you reconcile them on your Self Assessment return, where they usually produce a refund.
What expenses can a self-employed damp proofer claim?
You can claim your van running costs or mileage, injection equipment, drills and SDS bits, damp meters, hacking and rendering tools, damp-proof cream, membranes, salt-neutralising additives and consumables, PPE such as respirators, FFP3 masks, goggles, gloves and overalls, work lamps, generators, protective sheeting, a share of home-office and phone costs, trade insurance, CSCS card and training, and accountancy fees. Materials bought for a specific job and recharged to the client are also deductible against that income.
Do I get a tax refund as a damp proofing subcontractor?
Usually yes. CIS deductions are taken at 20% of your labour with no account for your £12,570 personal allowance or your allowable expenses. Once you file your Self Assessment and offset the personal allowance, your van, tools, PPE and materials, your actual tax bill is normally lower than the tax already deducted at source. The difference is repaid by HMRC. Many damp proofers see a refund of a few thousand pounds each year, so file promptly and keep every CIS deduction statement.
When does MTD for Income Tax apply to a damp proofer?
Making Tax Digital for Income Tax is mandatory from April 2026 for self-employed damp proofers with combined trading and property income over £50,000, from April 2027 above £30,000, and from April 2028 above £20,000. The test is on gross income, so your turnover including materials you recharge, not your profit. You will keep digital records and send HMRC quarterly summaries through compatible software, then a year-end finalisation that settles CIS deductions and any refund.
Does a damp proofer need to register for VAT?
Only once your taxable turnover passes £90,000 in any rolling 12-month period. A busy damp proofing one-person business handling large remedial jobs can reach this, especially when materials are included. If you mainly subcontract to VAT-registered builders, the domestic reverse charge usually applies to your construction services, meaning the contractor accounts for the VAT instead of you collecting it. This changes your cash flow and your invoices, so check whether the reverse charge applies before you register or raise a VAT invoice.
Sources
Official guidance on GOV.UK.